DOI: 10.1038/NMAT4166 SUPPLEMENTARY …...Sivaprakash Sengodan 1 †, Sihyuk Choi 1 †, Areum Jun ,...

SUPPLEMENTARY INFORMATIONDOI: 10.1038/NMAT4166

NATURE MATERIALS | www.nature.com/naturematerials 1

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SUPPLEMENTARY INFORMATION

Layered Oxygen Deficient Double Perovskite as an Efficient and Stable Anode

for Direct Hydrocarbon SOFCs

Sivaprakash Sengodan1†, Sihyuk Choi1†, Areum Jun1, Tae Ho Shin2, Young-Wan Ju1,

Hu Young Jeong3, Jeeyoung Shin4, John T.S Irvine2*, Guntae Kim1*

1 Department of Energy Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 689–

798, Korea

2School of Chemistry, University of St Andrews, St Andrews, Fife KY16 9ST, UK

3UNIST Central Research Facilities and School of Mechanical and Advanced Materials Engineering, UNIST,

Ulsan, 689–798, Korea

4 Department of Mechanical Engineering, Dong-Eui University, Busan 614-714, Korea

† These authors contributed equally to this work.

* Correspondence should be addressed to: [email protected] and [email protected]

Layered oxygen-deficient double perovskite as an efficient and stable anode for direct hydrocarbon solid oxide fuel cells

© 2014 Macmillan Publishers Limited. All rights reserved.

http://www.nature.com/doifinder/10.1038/nmat4166

2 NATURE MATERIALS | www.nature.com/naturematerials

SUPPLEMENTARY INFORMATION DOI: 10.1038/NMAT4166

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Methods

The Pr0.5Ba0.5MnO3 sample was prepared by the Pechini method. The desired composition

was obtained by dissolving nitrate salts of Pr, Ba, and Mn in distilled water with the addition

of quantitative amounts of citric acid and ethylene glycol. Upon removal of excess resin by

heating, a transparent organic resin containing metals in solid solution was formed. The resin

was slowly decomposed at 600 oC and calcined in air at 950 oC for 4 h. A-site layered PBMO

oxide anode obtained by annealing Pr0.5Ba0.5MnO3 oxide in H2 at 800 oC. The initial

structural characterization of the layered PBMO oxide was performed by X-ray

diffractometry by Rigaku diffractometer (Cu Kα radiation, 40 kV, 30 mA) and in-situ X-ray

diffraction (PANalytical Empyrean, Mo Kα radiation).

To measure the electrical conductivity and thermal expansion coefficient (TEC), the

powder of Pr0.5Ba0.5MnO3 was pressed into pellets, sintered at 1500 oC for 12 h. Electrical

conductivity was measured as a function of temperature using the standard four-probe

technique with a BioLogic Potentiostat. The electrical conductivity was measured in 5% H2

to convert Pr0.5Ba0.5MnO3 to layered PBMO and then that of layered PBMO was measured in

air atmosphere.

The oxygen non-stoichiometry at elevated temperature was studied through coulometric

titration (CT) by measuring the oxygen partial pressure of layered PBMO oxides as a

function of temperature, as reported elsewhere1. In the present case, an yttria-stabilised

zirconia (YSZ) tube (McDanel Advanced Ceramic Technologies, Z15410630) that is sealed

from the atmosphere is used. Ag paste (SPI Supplies, 05063-AB) is painted on the inner and

outer walls of the tube as electrodes. The potential across the membrane is given by the ratio

of the p(O2) outside and inside the cell according to the Nernst equation. Low pO2 in the tube





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is achieved by flowing gas mixtures composed of 10% H2-90% N2. The oxygen content can

be directly controlled by the electric charge passing through the YSZ tube. While

measurements were being performed the potential across the membrane (oxygen partial

pressure) is continuously monitored. When the potential across the membrane reaches the

stationary value 1 mV/h, the equilibrium between the sample and gas in the tube is

considered to be attained.

La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) powder was prepared by solid state reaction method

and dense electrolyte substrate was prepared by dry pressing and followed by sintering at

1475 oC. Stoichiometric amounts of La2O3 (Sigma 99.99%), SrCO3 (Sigma, 99.99%), Ga2O3

(Sigma, 99.99%), and MgO (Sigma, 99.9%) powders were ball milled in ethanol for 24 h.

After drying, the mixture was calcined for 6 h. The thickness of LSGM electrolyte was

adjusted about 300 m by polishing. LDC (La0.4Ce0.6O2−δ) was also prepared by ball milling

stoichiometric amounts of La2O3 and CeO2 (Sigma, 99.99%) in ethanol and then calcined for

6 h. For preparation of the anode slurry, Pr0.5Ba0.5MnO3 was mixed with an organic binder

(Heraeus V006) (1:2 weight ratio). NdBa0.5Sr0.5Co1.5Fe0.5O5+δ-Ce0.9Gd0.1O2−δ (NBSCF50-

GDC) cathode slurry was prepared by pre-calcined cathode and GDC powders (at a weight

ratio of 60:40) were mixed using ball milling, together with an organic binder. The electrode

slurries was applied on the LSGM pellet by screen printing method, and then fired at 950 oC

in air for 4 h. The porous electrode had active area of 0.36 cm2 and thickness about 20 m.

LDC layer was used as the buffer layer between the anode and the electrolyte to prevent

inter-diffusion of ionic species between PBMO and LSGM. 15 wt% of PBMO or Co0.5Fe0.5

(Co-Fe) catalyst solution was infiltrated onto the anode side and heated in air at 450 oC. For

fuel cell performance tests, the cells were mounted on alumina tubes with ceramic adhesives





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(Ceramabond 552, Aremco). Silver paste and silver wire were used for electrical connections

to both the anode and the cathode. The entire cell was placed inside a furnace and heated to

the desired temperature. V–i polarization curves were measured using a BioLogic Potentiostat

in the temperature range of 700-850 oC.





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Figure S1. The X-ray diffraction (XRD) patterns show (a) Pr0.5Ba0.5MnO3 and (b) layered

PBMO, respectively by Rigaku diffractometer (Cu Kα radiation, 40 kV, 30 mA).

Pr0.5Ba0.5MnO3 is synthesized at 950 oC in air which indicates a mixture of cubic (C) and

hexagonal (H) phase. The phase change from the Pr0.5Ba0.5MnO3 to the layered PBMO occurs

via reducing process in H2 at 800 oC.





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Figure S2. In-situ XRD patterns indicate phase change to layered PBMO in reducing

condition. The Pr0.5Ba0.5MnO3 was prepared with the calcination in air. In-situ XRD patterns

were measured with 200 oC intervals up to 800 oC in 5% H2 / 95% Ar gas flow. (PANalytical

Empyrean, Mo Kα radiation).





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Figure S3. TGA of layered PBMO was carried out in both air and reductive atmosphere with

a portion of coulometric titrated sample to estimate the absolute oxygen content. On heating

in air, the weight loss below 350 oC is probably due to desorption of water2 and no weight

loss happened from 400-800 oC under ramp heating process. Apparently, the layered PBMO

shows only a slight decrease or gain in weight compared to initial weight. In 5% H2 gas, it is

seen that the weight loss occurred in single sharp step around 400-650 oC. The weight loss in

the layered PBMO mostly attributed to the oxygen vacancy formation or decrease in the

oxygen content. The magnitude of weight loss at 700 oC is ~2.6 wt %, which agrees well with

the oxygen non-stoichiometric value ~2.49 wt % expected for O5-O5.75 transformation. A

slight weight gain for layered PBMO during cooling process may be due to the reoxidation of

the layered PBMO sample3.





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Figure S4. Sequential Thermal Expansion Measurements of layered PBMO as a function of

temperature and atmosphere (a), heating (1) to 900oC and cooling (2) in air ; (b), heating (3)

and cooling (4) in 5% H2; (c), heating (5) and cooling (6) again in in air, all at 2 oC min-1.

TEC for oxidised form 16.8(+/-0.2) x 10-6, TEC for reduced form 17.7 (+/-0.2) x 10-6.





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Figure S5. TGA of layered PBMO synthesized (a) in argon and (b) after oxygen uptake. On

heating in air, a similar reduction towards this layered double perovskite at 1050 oC, although

this is not complete by 1450 oC. After oxygen uptake PBMO sample shows no weight loss

below 1050 oC.





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Figure S6. I-V curves and the corresponding power densities of layered PBMO scaffold

without catalysts in H2.





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Figure S7. I-V curves and the corresponding power densities of layered PBMO with 15 wt %

PBMO catalyst in humidified H2.





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Figure S8. Short term stability for a layered PBMO with PBMO catalyst under a constant

current load of 1.0 A cm-2 at 700 oC in H2.





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PBMO catalyst in humidified C3H8.





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PBMO catalyst in humidified CH4.





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Figure S11. Impedance spectra of layered PBMO with PBMO catalyst using a humidified (3%

H2O) H2, 50 ppm H2S contaminated H2, C3H8, and CH4 at 850 oC.





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Figure S12. Microstructures of PBMO (a) without and (b) with infiltration after reduction.





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Figure S13. An off-line gas chromatograph (GC) was used to measure gas pyrolysis

reactions of propane with different temperatures from 700 to 850 oC. At fuel cell operating

temperatures, propane undergoes pyrolysis to form a H2, CH4, C2H4, C2H6 and other small

fragments.





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Figure S14. Final product gas composition by electrochemical reaction at a PBMO electrode

from 700 to 850 oC





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Co-Fe catalyst in humidified H2.





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Co-Fe catalyst in humidified C3H8.





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Co-Fe catalyst in humidified CH4.





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Figure S18. Impedance spectra of layered PBMO with Co-Fe catalyst using a humidified (3%

H2O) H2, 50 ppm H2S contaminated H2, C3H8, and CH4 at 850 oC.





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Figure S19. The current-voltage characteristics and the corresponding power densities of

layered PBMO with 15 wt % PBMO catalyst are investigated in various ppm H2S-

contaminated H2 at (a) 850 and (b) 800 oC. When the fuel was switched H2 containing 0, 30,

50, and 100 ppm H2S, the power density values of the layered PBMO with PBMO catalyst

are still 1.53, 1.45, 1.42, and 1.38 W cm-2 at 850 oC, respectively. At 800oC, the maximum

power densities are demonstrated 1.06, 1.05, 1.03, and 1.02 W cm-2 in H2 containing 0, 30, 50,

and 100 ppm H2S, respectively.





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Figure S20. The current-voltage characteristics and the corresponding power densities of

layered PBMO with 15 wt % Co-Fe catalyst are investigated in various ppm H2S-

contaminated H2 at (a) 850 and (b) 800 oC. When the fuel was switched H2 containing 0, 30,

50, and 100 ppm H2S, the power density values of the layered PBMO with PBMO catalyst

are still 1.77, 1.68, 1.64, and 1.59 W cm-2 at 850 oC, respectively. At 800oC, the maximum

power densities are demonstrated 1.42, 1.40, 1.38, and 1.33 W cm-2 in H2 containing 0, 30, 50,

and 100 ppm H2S, respectively.





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Figure 21. A cross sectional view of the (PBMO/LDC/LSGM/NBSCF-GDC) single cell is

provided. The thickness of the electrolyte is about 300 μm.





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Table S1. Amounts of gas for propane pyrolysis and final product gas by electrochemical

reaction from 700 to 850 oC

1000 L Temperature H2 (L) CH4 (L) C2H4(L) C2H6(L) CO(L) CO2(L)

Gas-phase pyrolysis

850 oC 194 441 260 26.4 1.96 1.34

800 oC 175 391 331 38.0 2.17 1.34

750 oC 133 255 205 25.2 1.84 1.84

700 oC 85.7 130 106 12.6 1.32 2.32

Final product gases

850 oC 176 337 253 20.9 46.8 13.1

800 oC 136 248 208 30.3 33.8 15.7

750 oC 91.4 152 125 12.1 22.3 15.0

700 oC 49.3 76.5 67.1 7.26 9.47 12.5





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References

1. Sengodan, S., Ahn, S., Shin, J., Kim, G. Oxidation–reduction behavior of

La0.8Sr0.2ScyMn1−yO3±δ (y=0.2, 0.3, 0.4): Defect structure, thermodynamic and

electrical properties. Solid State Ionics 228, 25-31 (2012).

2. Cumming, D. J., Kharton, V. V., Yaremchenko, A. A., Kovalevsky, A. V., Kilner, J. A.

Electrical Properties and Dimensional Stability of Ce-Doped SrTiO3- for Solid

Oxide Fuel Cell Applications J. Am. Ceram. Soc. 94, 2993-3000 (2011).

3. Tao, S., Irvine, J. T. S. Study on the structural and electrical properties of the double

perovskite oxide SrMn0.5Nb0.5O3−δ. J. Mater. Chem. 12, 2359-2360 (2002).



DOI: 10.1038/NMAT4166 SUPPLEMENTARY …...Sivaprakash Sengodan 1 †, Sihyuk Choi 1 †, Areum Jun ,...

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